I have always remembered having others inside, but according to our bookkeeper, we were 8 months old when the first split occurred. For us, there was neglect, and a large helping of phyiscal and sexual abuse happening, so I think my mind finally said "enough" and did what it needed to protect me... and the cycle began. It didnt take long before I was splitting every time something happened, or seemed like it was going to happen.
I hope that answers your questions...If not, feel free to ask for more info:)